This is the editor's interpretation of a paper published in the orthopaedic literature in 2017 - our attempt to make relevant medical articles accessible to lay readers. If you wish to read the original it is easy to ask your librarian to obtain a reprint for you from any medical library.

The authors feel that the progress of knowledge about anterior cruciate ligament (ACL) management over the last 100 years has not necessarily been linear, but has occasionally experienced a 'paradigm shift' where new understanding has changed accepted practice.

In the 1970s and 1980s open primary repair was the most common treatment - ie the knee was surgically opened after the injury and the torn ends of the ligament were brought back into contact and maintained until healing of the torn ends occurred. Mid-term follow up studies as well as some randomised clinical trials showed, however, that the results of this procedure were not particularly good, and repair was largely abandoned in favour of reconstruction.

"At the end of the primary repair era, however, several studies showed that outcomes of open primary repair were good to excellent and did not deteriorate when this technique was selectively performed in patients with proximal ACL tears (ie at the upper end of the ligament where it had peeled off from its attachment to the femur), whereas primary repair led to disappointing and unpredictable results in patients with mid-substance tears." This proximal 'peel off' type of injury usually has excellent tissue quality, whereas mid-ligament tears often end of with a ragged 'mop-end' of torn fibres. Unfortunately, enrollment of patients in the randomised trials was already finished, ultimately leading to abandoning of open primary repair.

The authors note that it "seems that, when the decision was made to abandon primary repair due to marginal results, the surgical community did not recognize the role of tear location on the outcomes of primary repair." They identify many reasons why this might have occurred:

difficulty keeping up with surgical literature - online search engines were still rudimentary

language problems - nowadays it is easy to obtain online translations from various languages

difficulties of nomenclature in publications - where there was less standarisation of the names for surgical procedures than there is now

So, they conclude, "not all studies may have been used to make a well-informed decision regarding the abandonment of primary ACL repair for all patients instead of only abandoning this technique for mid-substance tears." Things were further complicated because in the 80s surgeons were turning from opening up the knee for surgery to trying to operate via arthroscopy (keyhole surgery). Some of the poor results of the early phase may have related to this bigger procedure as well as the long period after surgery when the knee was immobilised. The 80s also represent a period when surgeons were taking a keen interest in rehabilitation after ACL surgery, because the rehabilitation regime also made a difference to the outcomes. By the 1990s primary repair through the arthroscope was feasible - instrumentation was well developed and surgeon skills were developing, but by this time the procedure of primary repair had to a large extent already been abandoned.

So the 1990s was dominated by arthroscopic reconstruction being the common surgical technique, and rehabilitation was improving from the older periods of 6-8 weeks in a cast to a more rapid rehabilitation - because the long periods of keeping the leg still led to pain during rehabilitation, loss of range of motion and decreased function. In the three decades since the 1990s, reconstruction techniques have improved and so have regimes of rehabilitation, but no-one will know how well the repair patients might have done if surgery had been done through the arthroscope and the patients had had current accelerated rehabiitation and not been immobilised for so long.

So two decades where possible progress in understanding has effectively been lost, and only now - with MRI being so readily available, arthroscopic instrumentation and understanding being so well advanced, and rehabilitation being so well understood - are surgeons starting to look again at repair. In 2015 Dr Greg DiFelice and his team reported on a cohort of 11 patients with proximal tears who he had treated with primary repair, not reconstruction, and they found excellent results at a mean of 3.5-years follow-up. There have been a number of articles published since then that have demonstrated similar findings. Professor Gordon Mackay 's team also found that using a braided polymer 'internal brace' lent support to the healing ligament during the rehabilitation phase. A team under Professor Adrian Wilson had had excellent results with the internal brace in children.

[Ed: what needs to be pointed out is the within the normal ACL ligament are sensory 'proprioceptive' fibres, aid the knee in position sense, and these fibres are largely retained in repairs and largely lost in reconstructions.]